The instant Application relates generally to fuel injection systems and more particularly to mechanically or electrically operated diesel fuel injectors having means for separately regulating each of the functions of timing of fuel injection and metering of fuel into the injector thereby permitting separate and independent adjustment to both the timing of fuel injection into an engine and the quantity of fuel metered into the fuel injector prior to injection. U.S. Pat. Nos. 4,235,374 to Walter et al which issued Nov. 25, 1978 and 4,281,792 to Sisson et al which issued Aug. 4, 1971 disclose a single solenoid fuel injector. This fuel injector injects metered quantities of fuel into the cylinders of a diesel engine as well as to function as an engine driven pump to pressurize the fuel prior to injection into the engine. The above noted United States patents disclose a fuel injector which utilizes a primary pumping piston disposed to be actuated by a cam operated mechanism, a metering or floating piston slidably mounted within the interior of the injector and a nozzle portion contiguous with fuel injector or combustion chamber of the engine. A timing chamber is formed between the primary pumping piston and the metering piston. The injector includes a cooperating electronic control unit (ECU) which generates a signal to control the state of a single electronically controlled solenoid which when in an open condition permits fuel to flow into the timing chamber and which when closed initiates fuel injection. In addition to the formation of the timing chamber between the pumping piston and the metering piston, a metering chamber is formed between the lower portion of the metering piston and the bore which houses the floating piston. The quantity of fuel fed to the metering chamber determines the amount of fuel which thereafter will be injected into each engine cylinder. The control valve is utilized to control both the timing of injection and the quantity of fuel metered to the engine. In the above patents, a substantially unobstructed fuel passage is provided from a supply to the metering chamber. Consequently, the amount of fuel that resides within the metering chamber is determined by the volume of the metering chamber, hence, this method of metering has been called volumetric fuel metering. During the metering mode of operation of the Walter et al or the Sisson et al injectors, the pumping piston is caused to retract allowing the supply pressure in the metering chamber to force the metering piston upward to follow the pumping piston retraction. This causes the volume of the metering chamber to be increased. To terminate the metering process the control valve is opened allowing supply fuel to flow into the timing chamber, thereby breaking the hydraulic link between the two pistons. A spring is inserted within the timing chamber to bias the two pistons apart to insure that the motion of the metering piston is stopped and that no more fuel enters the metering chamber. The utilization of the spring within the metering piston increases the length of the injector therein consuming valuable engine space. It should be recalled that a unit injector is typically incorporated within the engine and driven by the cam shaft of the engine.
The above noted fuel injectors are relatively complex in that they utilize check valves within the movable metering piston, in particular, a timing chamber check valve and a metering chamber check valve which are included within the movable floating or metering piston. The incorporation of the check valves within the moving element complicates the manufacture and assembly of the above noted fuel injectors and may cause non-repeatability in the injector performance. During the dumping mode of operation of these fuel injectors, fuel is dumped from the timing chamber to drain through the timing chamber check valve. By dumping the timing chamber through the restriction imposed by the check valve slows the dumping process.
It is therefore an object of the present invention to provide a unit injector having a less massive metering piston to permit a more rapid initiation of the injection mode of operation. In addition, it is an object of the present invention to provide a unit injector having a shorter metering piston thus providing a more compact design. A further object of the present invention is to eliminate the check valves from the influence of the movable metering piston and to eliminate the necessity for the timing chamber check valve and biasing spring. Another object of the invention is to provide a unit injector having one dump port and to hydraulically bias the needle valve, with the dumped fuel to rapidly terminate injection.
Accordingly, the invention comprises: a fuel injector comprising: a body having an axially extending bore, a pumping piston and a remotely positioned metering piston positioned within the bore. A timing chamber is defined within the bore between the pumping piston and the metering piston and a metering chamber defined between the metering piston and the lower portion of the bore. The injector includes first fuel passage having an electronically controlled valve situated therein for receiving pressurized fuel and for controllably transmitting the fuel to the timing chamber; a second fuel passage having a pressure regulator for receiving pressurized fuel for establishing the pressure level for fuel in the metering chamber and for transporting the received fuel to the metering chamber. The injector further includes a spring chamber and nozzle situated remotely from the metering chamber wherein the nozzle partially extends within the spring chamber. A biasing spring is located within the spring chamber for biasing the nozzle in a closed position during non-injecting modes of operation. The injector further includes a third fuel passage terminating at an open end at the wall of the bore, proximate said timing chamber forming in cooperation with the bore, a timing chamber dump port. The third fuel passage also communicates with the spring chamber and with a fourth passage having a restrictive orifice situated therein for establishing upstream thereto an increased pressure during the period of time that fuel in the timing chamber is being dumped through.